1) Field of the Invention
This invention relates to a laminated sheet for a lid of a container for instant food cooked with hot water and more particularly to a laminated sheet for a lid of a container usable for various instant foods such as noodles, which are cooked for eating simply by pouring hot water into the container.
2) Description of the Background Art
Conventionally, a lid of a container for instant food cooked with hot water is made of a laminated sheet which is composed of an aluminum foil and a paper affixed to the foil.
As shown in FIG. 3, for cooking this type of instant food, a lid a is firstly peeled off from the opening of a container b which contains instant food to be cooked, and hot water is poured into the container b. The peeled portion of the lid a is then bent toward the opening of the container b to seal the opening of the container b therewith, and the container b is allowed to stand for a few minutes to cook the instant food with hot water.
The conventional lid a, however, has a disadvantage in that the lid a curls upward due to the hot steam when hot water is poured into the container b, which leads to insufficient sealing of the opening of the container b. Therefore, it is normal practice that consumers put a plate or the like on the lid a as a weight, or the lid a is fixed to the container b with an adhesive tape.
Under the above circumstances, the present inventors have carried out studies, and have found that, in the case where a paper is used as an upper layer and affixed to the upper face of an aluminum foil to constitute a lid, the lid curls upward when hot water is poured into a container, because contraction of the paper due to emission of humidity therefrom is larger than the difference in thermal expansion rate between the aluminum foil and the paper, and that, in the Case where a paper is used as a lower layer and affixed to the lower face of an aluminum foil to constitute a lid, the lid curls upward when hot water is poured into a container, because expansion of the paper due to absorption of water is larger than the difference in thermal expansion rate between the aluminum foil and the paper. The present inventors have also found that the undesirable effect of water can be eliminated by using a synthetic paper, and that a desired sealing property of a lid can be obtained by making use of the difference in thermal expansion rate between a metallic foil and a synthetic paper. The present invention has been accomplished based upon these findings.